In many types of printing, particularly flexographic printing, offset printing and screen printing, there is an advantage in using seamless sleeves as printing elements instead of plates wrapped around printing cylinders. Seamless sleeves allow printing of continuous patterns. The use of seamless sleeves allows printing presses to operate in a smoother manner. Before a sleeve can be mounted on a printing press it has to be imaged and processed, although some materials are available today which do not require processing. The printing sleeves 116 are imaged on laser imaging device 100 as is shown in FIG. 1.
Such machines have a mandrel 108 on which a printing sleeve 116 is mounted directly. The mandrel 108 is secured in the imaging device 100 at two ends by a tail stock 104 and a head stock 144. A laser imaging head 120 is adapted to travel along the longitudinal axis of the printing sleeve 116 on imaging head tracks 124, controlled by lead screw 128.
Printing sleeve 116 is loaded over the mandrel 108. The printing sleeve 116 may be a thin-walled metal or composite cylindrical tube with media applied to the outer surface. The mandrel 108 may be provided with a number of air holes 112 in its surface through which air can be forced. This air flow creates an air bearing over mandrel 108 and permits printing sleeve 116 to be floated on a cushion of air onto the mandrel 108, the air expanding printing sleeve 116 to enable easy loading and positioning. The air is supplied by air source 140 through air hose 136. Air hose 136 is fixed to air source 140 on one side and to air inlet 132 on mandrel 108 on the other side of the air hose 136. When the supply of forced air is discontinued, printing sleeve 116 contracts to form a tight fit with mandrel 108.
Mandrel 108 is heavy and rotates at high speed. It is important, therefore, that the mandrel be securely attached at both ends. Detecting whether the mandrel 108 is securely fastened to both the trail stock 104 and head stock 144 is necessary to prevent problems during normal operation of imaging device 100.